1. Field of the Invention
This invention relates to a substrate processing apparatus, and more particularly to a substrate processing apparatus useful for forming, for example by electroless plating, an interconnects-protective layer on the exposed surface of embedded interconnects which have been formed by embedding an electric conductor, such as copper, silver or gold, in fine recesses for interconnects formed in the surface of a substrate, especially a semiconductor wafer.
2. Description of the Related Art
As a process for forming interconnects in a semiconductor device, the so-called xe2x80x9cdamascene processxe2x80x9d, which comprises embedding a metal (electric conductor) into trenches for interconnects and contact holes, is coming into practical use. According to this process, aluminum, or more recently a metal such as silver or copper, is embedded into trenches for interconnects and contact holes previously formed in the interlevel dielectric of a semiconductor substrate. Thereafter, an extra metal is removed by chemical mechanical polishing (CMP) so as to flatten the surface of the substrate.
In the case of interconnects formed by such a process, for example copper interconnects formed by using copper as an interconnect material, the embedded copper interconnects have an exposed surface after the flattening processing. In order to prevent thermal diffusion of such interconnects (copper), or to prevent oxidation of such interconnects (copper) e.g. in forming thereon an insulating film (oxide film) under an oxidizing atmosphere to produce a semiconductor device having a multi-layer interconnect structure, it is now under study to selectively cover the exposed surface of interconnects with an interconnects-protective layer (cap material) composed of a Co alloy, a Ni alloy or the like so as to prevent thermal diffusion and oxidation of the interconnects. Such an interconnects-protective layer of a Co alloy, a Ni alloy or the like can be produced e.g. by electroless plating.
As shown in FIG. 20, fine recesses 4 are formed in an insulating film 2 of SiO2 or the like which has been deposited on the surface of a substrate W such as a semiconductor wafer. A barrier layer 6 of TaN or the like is formed on the entire surface, and then copper plating, for example, is carried out onto the surface of the substrate W to fill the fine recesses 4 with copper and deposit a copper film on the insulating film. Thereafter, CMP (chemical mechanical polishing) is carried out onto the surface of the substrate W so as to flatten the surface, thereby forming interconnects 8 composed of a copper film in the insulating film 2. Thereafter, an interconnects-protective layer (cap material) 9 composed of a Coxe2x80x94Wxe2x80x94P alloy film is formed e.g. by electroless plating selectively on the surface of the interconnects (copper film) 8 to protect the interconnects 8.
A common electroless plating method for the selective formation of the interconnects-protective layer (cap material) 9 of Coxe2x80x94Wxe2x80x94P alloy film on the surface of interconnects 8 generally involves the following process steps: First, the substrate W such as a semiconductor wafer, which has undergone the CMP treatment, is immersed in an acid solution e.g. of 0.5M H2SO4 at a solution temperature of e.g. 25xc2x0 C. for e.g. one minute to remove CMP residues, such as copper, remaining on the surface of the insulating film 2. After cleaning the surface of the substrate W with a cleaning liquid such as ultrapure water, the substrate W is immersed in a mixed solution, e.g. of 0.005 g/L PdCl2 and 0.2 ml/L HCl, at the solution temperature of e.g. 25xc2x0 C. for e.g. one minute to adhere Pd as a catalyst to the surface of interconnects 8, thereby activating the exposed surface of interconnects 8. Next, after cleaning the surface of the substrate W with a cleaning liquid such as ultrapure water, the substrate W is immersed in a solution containing e.g. 20 g/L of Na3C6H5O7.2H2O (sodium citrate) at the solution temperature of e.g. 25xc2x0 C., thereby carrying out neutralization treatment of the surface of interconnects 8. Thereafter, after washing the surface of the substrate W with ultrapure water, the substrate W is immersed in a Coxe2x80x94Wxe2x80x94P plating solution at a solution temperature of e.g. 80xc2x0 C. for e.g. 120 seconds, thereby carrying out selective electroless plating (electroless Coxe2x80x94Wxe2x80x94P cap plating) onto the activated surface of interconnects 8. Thereafter, the surface of the substrate W is cleaned with a cleaning liquid such as ultrapure water. The interconnects-protective layer 9 composed of a Coxe2x80x94Wxe2x80x94P alloy film is thus formed selectively on the surface of interconnects 8 to protect the interconnects 8.
When forming such an interconnects-protective layer (cap material) composed of a Coxe2x80x94Wxe2x80x94P alloy film by electroless plating, as described above, a catalyst-imparting treatment for imparting a catalyst, such as Pd, to the surface of interconnects is carried out. Further, in order to prevent an interconnects-protective layer from being formed on an insulating film, it is necessary to remove CMP residues, such as copper, remaining on the surface of the insulating film. Removal of such residues is generally practiced by using an inorganic acid such as H2SO4 or HCl. On the other hand, an alkaline solution is generally used as an electroless plating solution. Accordingly, it is necessary to provide a neutralization step immediately before an electroless plating treatment to stabilize the plating process. A number of pretreatment steps, before an electroless plating step, are thus necessary, and a number of treatment baths for carrying out the steps are needed. This will lead to a low throughput and a complicated process control for the respective steps. Moreover, the total facilities should necessarily be large and a wide installation space in a clean room will be required, leading to a high cost for clean room.
The present invention has been made in view of the above situation in the related art. It is therefore an object of the present invention to provide a substrate processing apparatus which can efficiently form an interconnects-protective layer, for example, on the surface of a substrate at a low initial cost for apparatus and a low running cost without the need for a wide installation space.
In order to achieve the above object, the present invention provides a substrate processing apparatus comprising a loading/unloading and cleaning area accommodating a first transfer robot which has a hand adapted for handling of a dry substrate and a hand adapted for handling of a wet substrate, a loading port which loads a substrate cassette that houses a substrate, and a cleaning unit for cleaning a substrate. A plating treatment area accommodating a second transfer robot which has a back surface-attracting type of hand provided with a reversing mechanism, a pretreatment unit for carrying out a pretreatment of a substrate before plating, and a plating treatment unit for carrying out a plating treatment of the substrate.
By thus dividing the interior of the apparatus into two areas, i.e. the loading/unloading and cleaning area and the plating treatment area, and providing the areas with the first and second transfer robots, respectively, each having a hand or hands meeting the process requirements of the respective area, the process steps for the formation of an interconnects-protective film e.g. by electroless plating can be carried out consecutively in one apparatus. Accordingly, as compared to the case of carrying out the respective process steps in separate apparatuses, the total facilities can be made compact and a wide installation space is not needed. Further, the initial cost for the apparatus and the running cost can be reduced. In addition, an interconnects-protective film can be formed in a short time.
In the substrate processing apparatus, the pressures in the two areas can be set as follows: pressure in the loading/unloading and cleaning area greater than  pressure in the plating treatment area. Further, the pressure in the loading/unloading and cleaning area can be set to be lower than the pressure in a clean room. This can prevent air in the plating treatment area from flowing into the loading/unloading and cleaning area, and can also prevent air in the loading/unloading and cleaning area from flowing into the clean room.
A temporary storage stage may be provided in the loading/unloading and cleaning area. In this case, the first transfer robot can transfer a substrate between the substrate cassette, the cleaning unit and the temporary storage stage.
A roll brush cleaning unit and a spin-drying unit, for example, may be provided as the cleaning unit in the loading/unloading and cleaning area. This makes it possible to subject a substrate, which has undergone a treatment such as electroless plating, to a two-step cleaning in a consecutive manner and spin-dry the substrate.
The second transfer robot can transfer a substrate between the temporary storage stage, the pretreatment unit and the plating treatment unit. The provision of the reversing mechanism in the hand of the second transfer robot eliminates the need for separately providing an independent reversing mechanism and thus can simplify the apparatus.
A pre-cleaning unit for carrying out pre-cleaning of a substrate, a first pretreatment unit for imparting a catalyst to the surface of the substrate and a second pretreatment unit for carrying out a chemical liquid treatment of the catalyst-imparted surface of the substrate, for example, may be provided as the pretreatment unit in the plating treatment area.
The plating treatment area may also be provided with an inter-plating cleaning unit as the pretreatment unit for carrying out cleaning of a substrate in the waiting time between plating treatments.